International Mobile Equipment Identity (IMEI) consists of 15 digits, and is commonly known as serial number and stored in an EEPROM. Each mobile terminal corresponds to a unique IMEI, and will be written with a unique IMEI when assembled and delivered from the factory. From production to delivery, the IMEI will be recorded by manufacturing vendors, and it is also the archive number and ID number of said mobile terminal at the manufacturer side.
IMEI consists of TAO+FAC+SNR+SP.
1, the first six digits (TAO) are the type approval number, generally representing the model,
2, the following two digits (FAC) are the final assembling number, usually representing the origin,
3, the following 6 digits (SNR) is a string number, generally representing the production serial number,
4, the last digit (SP) is usually 0, representing the check code.
In the standby screen, inputting *#06# can check the IMEI. Only a mobile terminal having an IMEI can be used in the GSM/UMTS/LTE network, and the operators can identify the device type according to the IMEI, and then provide related services, users can also make use of the IMEI to determine whether the purchased mobile terminal is an original production or not.
Since the IMEI of said mobile terminal is written in a Flash that can be repeatedly read and written, it will be relatively easy to be modified by computer programs to deceive the network to obtain illegal status or function, thus the IMEI protection would be included within the requirements of the operator.
The related design idea proposed aiming to the IMEI protection is to use the IMEI and the device parameters to generate the checked value with the relevant algorithm and store it in an one-time programmable (OTP) region, at each time of starting up the host, said checked value will be compared, and the usage is limited if they are different; or use an external device, and said external device encrypts the IMEI with a certain encryption algorithm to form into the ciphertext which is stored together with the decryption key in said OTP region, and accesses to the plaintext data after decrypting the ciphertext with the decryption key, and then connects with the communication terminal to verify.
The abovementioned technique has the following problem: the way of protecting the IMEI is too complicated, increasing the difficulty of implementation, or it needs to use an external device to protect the IMEI, so that the mobile terminal is not convenient to use.